One can use test data directly with the Response Function Hyperelastic model. This does not require any curve-fitting and will use the data exactly. One would separate and enter the uniaxial tension and compression data directly. One also need to define the compressibility either by including pressure-volume test data or specifying the material compressibility parameter. Details of the Response Function Hyperelastic model can be found in the ANSYS Help sections below: https://ansyshelp.ansys.com/account/secured?returnurl=/Views/Secured/corp/v190/ans_mat/aQw8sq22dldm.html%23respfunc_mat Curve-fit to hyperelastic model: If one wish to perform curve-fitting on predefined hyperelastic models,then include both compression and tension in the “uniaxial test data”. Be sure to just put the values in ascending order, and there should be a (0,0) data point.